1. Field of the Invention
Tractor trailer assemblies, or big rigs, as they are often referred to, are designed and built to carry the loads allowed by law and more. Those loads may vary to from state to state, but typically do not vary greatly from the rules established by the Federal Department of Transportation.
While a load may be within the legal limit, its character may result in an imbalance which often overloads one axle as opposed to another. For example, if the load is particulate material, e.g., grains, it tends to shift forward as the rig brakes. Since the rig will necessarily accelerate slowly, such a load is much less likely to shift toward the rear.
The use of devices which add an additional axle to the tractor trailer rig have been known for more than 40 years. Such devices, sometimes referred to as dollies, have a variety of uses, including, but not limited to, adding a load bearing axle to a tractor and to permit a coupling for the towing of a rear trailer or pup. The actual coupling of the dolly is a source of difficulty. It is essential that the coupling is sufficiently firm so as to permit the driver to control it while in motion and sufficiently simple as to permit free use of the fifth wheel secured to the frame of the tractor when the dolly is secured thereto.
It is the intent and purpose of the present invention to provide a dolly which is readily controlled by the driver of a rig and which will supplement the load bearing capacity of an axle which may otherwise become overloaded.
2. Overview of the Prior Art
The existence and use of dollies by the trucking industry is somewhat common, although not in extensive use. In some instances it is used to convert a two axle tractor to a three axle tractor, primarily to add to the load bearing capacity of the rig. In other instances, dollies provide the means of hooking up a second trailer behind the trailer engaged at the tractor. While similar in use, the dolly of the present invention offers the trucking industry heretofore unavailable control and versatility.
Exemplary of what is currently available to the industry is the 1966 patent to Fontaine, U.S. Pat. No. 3,413,015. Fontaine is one of several attached dollies, including, but not limited to Neff et al. U.S. Pat. No. 3,827,723; Cunha U.S. Pat. No. 3,476,405; Barker et al. U.S. Pat. No. 3,421,778, and Lankenau U.S. Pat. No. 3,764,164, all of which employ a tongue and eye system for engagement with the tractor of a rig, or the trailer being towed thereby.
While Fontaine offers guide members in an attempt to stabilize the tongue, in general, the use of a tongue and eye potentially involves considerable lack of stability and is difficult to hook up. While the referenced patents are vintage 60's and 70's, the tongue and eye concept is current today.